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Every website returns 'Your connection is not secure'

josh6426
josh6426

Every time I log onto any website (Google, YouTube, even Mozilla Support), I receive the 'SEC_ERROR_UNKNOWN_ISSUER' HSTS error. My date and time is correct, I use AVG (turning it off does nothing either), Microsoft Family Safety is off (and never has been on), and there is no malware on my system. I checked into the Certificate Viewer ( as shown in https://support.mozilla.org/en-US/questions/1130326 ) and noticed that the 'Issued To' CN and the 'Issued From' CNs are identical - not right. In addition, the Certificate Hierarchy is the CN too.

Every time I log onto any website (Google, YouTube, even Mozilla Support), I receive the 'SEC_ERROR_UNKNOWN_ISSUER' HSTS error. My date and time is correct, I use AVG (turning it off does nothing either), Microsoft Family Safety is off (and never has been on), and there is no malware on my system. I checked into the Certificate Viewer ( as shown in https://support.mozilla.org/en-US/questions/1130326 ) and noticed that the 'Issued To' CN and the 'Issued From' CNs are identical - not right. In addition, the Certificate Hierarchy is the CN too.

Modified by josh6426

Chosen solution

You can check the connection settings.

  • Options/Preferences -> General -> Network: Connection -> Settings

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems.

See also:

Read this answer in context 👍 0

All Replies (5)

josh6426
josh6426 Question owner

Here are screenshots of the Certificate Viewer

cor-el
cor-el
  • Moderator

Chosen Solution

You can check the connection settings.

  • Options/Preferences -> General -> Network: Connection -> Settings

If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly.

See "Firefox connection settings":

Boot the computer in Windows Safe mode with network support to see if that has effect in case security software is causing problems.

See also:

jscher2000 - Support Volunteer
jscher2000 - Support Volunteer
  • Top 10 Contributor

Weird, that's my website. I use Let's Encrypt, so definitely the cert is fake.

There was a similar thread earlier today where setting No Proxy helped. That doesn't really address the reason for the man in the middle, though. (https://support.mozilla.org/questions/1190762)

That setting is here:

  • Windows: "3-bar" menu button (or Tools menu) > Options
  • Mac: "3-bar" menu button (or Firefox menu) > Preferences
  • Linux: "3-bar" menu button (or Edit menu) > Preferences
  • Any system: type or paste about:preferences into the address bar and press Enter/Return to load it

Firefox 56-58: In the search box at the top of the page on the right side, type proxy and Firefox should filter to the "Settings" button, which you can click.

Firefox 38-55: In the left column, click Advanced. Then on the right side, with the "Network" mini-tab active, click the "Settings" button.

In All Versions: The default of "Use system proxy settings" piggybacks on your Windows/IE "LAN" setting. "Auto-detect" can lead to a flaky connection. You may want to try "No proxy".

Any difference?

josh6426
josh6426 Question owner

Thanks. Converting to 'No Proxy' worked perfectly. Thanks a lot for your help, guys. Would've been doomed alone.

Modified by josh6426

jscher2000 - Support Volunteer
jscher2000 - Support Volunteer
  • Top 10 Contributor

Thanks for reporting back. I'm concerned about what was hijacking your connection and whether it may still be on your system. I think the easiest way to investigate that would be to use the cleaning tools listed in our support article: Troubleshoot Firefox issues caused by malware. Those are free or have a free trial. There also are forums listed for stubborn cases.